In recent years, printers using sprayable inks, such as the ink jet printer, have come into general use. These printers, which employ ink jet heads having small orifices that propel inks in a continuous stream of drops or in minute individual drops on demand, are used in various electronic printing applications. They offer not only high speed but quiet operation without the need for external developing or fixation procedures. Further, through the use of multiple ink jet heads, various colors may be obtained suitable for computer graphics applications; for example, the printing or plotting of bar charts, graphs, pie charts and the like benefit from color differentiation.
Because of the simplicity and economy of ink jet film printing, this imaging process holds promise for growth beyond transparency making. Wide-format electronic printing of engineering and architectural designs is a natural expansion of ink jet printing. Office systems applications which include publications and promotional materials is another. These applications go beyond the normal clear or transparent films and require film supports and coating composites that are tailored to new end uses.
Ink jet systems employed in informational electronic printing are comprised of three components: the printer, the ink and the receptor sheet. The printer controls the size, number and placement of the ink droplets and contains the transport system. The ink provides the colorants which form the image, and the receptor sheet provides the medium which accepts and holds the ink. The quality and archivability of ink jet prints is a function of the total system. However, the composition and interaction of the ink and the receptor material most affect the quality and archivability of the imaged product.
Ink compositions which are useful in ink jet recording systems are well known and generally contain water, organic solvents and dyes. There is thus disclosed, for example, in European Patent 0,294,155, an ink jet composition useful in ink jet recording consisting of water based vehicle containing about 30-99% wt. water with the balance made up of high boiling solvents such as glycol, glycol ethers, pyrrolidones and amides. The inks contain preferably acid or direct dyes.
In present practice, ink jet systems fall broadly into two categories; those that employ high organic solvent-water based inks, and those that are essentially aqueous. Aqueous inks normally contain up to 10% of a high boiling solvent such as diethylene glycol, whereas high organic solvent inks contain, in addition to water, about 50% of a high boiling organic solvent such as diethylene glycol. The imagery of both of these types of ink has poor water resistance (i.e., the dye image leaches out or the image layer containing the dye dissolves). Additionally, the dye image is prone to smudging.
While earlier ink jet printing applications employed paper, presentation films such as overhead projection transparencies soon found favor because of the simplicity and economy of their preparation. However the design requirements of film and film-like surfaces differ from those of paper and are much more difficult to meet. Despite improvements in ink jet film compositions, there remain problems which inhibit the realization of the full potential of ink jet printing.
Ink jet film compositions are normally sensitive to water and their imagery can dissolve and leach out. Also, under humid conditions, their imagery can bleed thereby losing definition, all the more when the inks employ high boiling solvents such as the glycols. Conventional ink jet prints often lack light resistance and good file aging properties. All the above shortcomings require resolution to achieve good print archivability.
Polymeric films for use as recording media represent a special problem in ink jet recording because their surfaces are hydrophobic or quasi-hydrophobic. Even when their surfaces are treated with special coatings to accept and absorb the inks, it is difficult to obtain the requisite qualities of image density and resolution without incurring tack, smear, image bleed, water solubilization of the ink receptive matrix, or other undesirable properties.
The use of water/glycol ink systems presents a special problem. At high humidities, a phenomenon described as image bleed, occurs. The ink jet printer applies small ink droplets in a selective pattern to form the images. These droplets are absorbed into the coating on the film surface to form dots. After initial absorption, the dye continues to spread laterally. Some post imaging spread is desirable to fill in the white areas between the dots and obtain good image density. At high humidities, however, this spreading continues and causes the image to spread excessively, that is, to bleed thereby losing image sharpness or resolution. Ink vehicles which do not contain high boiling solvents such as glycol do not exhibit this level of image bleed.
There is considerable literature which describes attempts to provide the optimal receptor sheet. Approaches to the problem of hydrophobic surfaces include use of polymers alone or in admixture as ink receptive coatings; see for example, U.S. Pat. Nos. 4,503,111; 3,889,270; 84,564,560; 4,555,437 and 4,578,285. Multiple coatings have also been employed in trying to overcome the various problems associated with hydrophobic nature of recording media; illustrative of these coatings are U.S. Pat. No. 4,379,804, Japanese Patent Number 01041589 and Japanese Disclosure Numbers 86-132377; 86-074879 and 86-41549. Additionally, the use of mordants to help fix the dye and minimize bleed has been the subject of a number of patents, including U.S. Pat. Nos. 4,554,181; 4,578,285 and 4,547,405.